The present invention relates to a plural test mode selection circuit of a semiconductor device, particularly to a plural test mode selection circuit capable of extending a number of option modes by using a general address/control pad.
In general, a semiconductor device is manufactured so as to execute an operation of a particular mode in order to facilitate the evaluation of a chip in accordance with the tendency of increasing integration and reliability of the semiconductor product. That is to say, it is formed to operate by selecting any one of various option modes such as redundancy trimming, a die information adding function, an electrical characteristic evaluating function, and the like. It has been achieved either by using additionally a preparatory pad or by adding a high voltage sensing circuit to an address/control pad to select one option mode, used for evaluating the characteristics of a semiconductor chip, other than a general READ/WRITE operating mode of a semiconductor device.
In the above description, according to the former method, a preparatory pad which is to usually used is provided, and a particular mode can be selected by applying a power source to the preparatory pad in a wafer state. Thus, there are required as many preparatory pads as the number of the option modes because of selecting only one particular mode by one of the preparatory pads. And, the latter method utilizing a high voltage sensing circuit is constructed so as to select a particular mode by connecting the high voltage sensing circuit and the address/control pad. That is to say, when a high voltage (12-14 volts) is applied to a pad coupled with the high voltage sensing circuit, the high voltage sensing circuit is enabled and the particular mode is selected thereto. Therefore, it has been constructed such that only one particular mode can be selected by a single pad and the high voltage sensing circuit attached thereto.
Therefore, since the former method of applying the preparatory pad generally requires as many preparatory pads as the number of option modes, the dimension of a chip becomes larger. Further, when it is made in a package, there has been a problem that any particular mode can not be selected because the preparatory pads can not be bonded to each other. Moreover, the latter method of adding a high voltage sensing circuit to an address/control pad has rendered a problem that is hard to extend the number of option modes because only one particular mode is selected by one pad and one high voltage sensing circuit.
Therefore, an object of the present invention is to provide a plural test mode selection circuit capable of selecting a particular option mode by applying a high-voltage power source, by adding a high voltage sensing circuit to a part of the address/control pads used in a general read/write operation, and by applying a control signal and an address signal of CMOS/TTL level to the address/control pad without the high voltage sensing circuit.
Another object of the present invention is to provide a plural test mode selection circuit capable of extending the number of option modes by combination of one high-voltage source and other input signals.
To achieve the objects as described above, the plural test mode selection circuit for use in a semiconductor integrated circuit having a plurality of test modes, includes:
first, second, third, fourth and fifth address/control pads for inputting each externally applied voltage;
first, second, third, fourth and fifth buffers each connected with the pads, for buffering the address/control signals from each pad;
slave decoder connected with the second and third buffer circuit for producing a sub-mode signal;
master decoder connected with the fourth and fifth buffer circuit, for producing a main-mode signal;
mode selector connected with the slave decoder and master decoder, for selecting a particular mode; and
high-voltage sensing circuit for enabling the mode selector only when a voltage applied from an exterior source reaches a particular voltage, whose input is connected to the first pad and output is connected to the mode selector.